The invention relates to an energy guiding chain for housing and guiding energy transmission lines between a fixed base and a mobile driver. The chain comprises two parallel plate-link lines consisting of plate-links which are opposite to each other in a crosswise direction and connected by means of transverse links. Those plate-links of each plate-link line which are directly adjacent can be pivoted in relation to each other in the direction of bending of the chain and the chain forms a deflection area. At least in an area of the chain adjacent to the driver, the chain links are linked to each other in such a manner as to resist stretching under tension in several sections by means of at least one element which is substantially inextensible in the longitudinal direction of the chain and is flexible in the direction of bending of the chain.
Today, energy guiding chains of this kind are largely made of plastic. Polyamides are a preferred plastic. Polyamides are hygroscopic, however, and like other plastic materials have the disadvantage that they have a relatively high coefficient of expansion in very humid and hot environments.
Energy guiding chains are used in different lengths and sizes under various conditions, such as in very humid and hot rooms or buildings. In long chains, the relatively high additional loads resulting from the energy transmission lines housed inside the chains cause high tensile and thrust stresses when the chain travels. In very hot rooms or buildings with high humidity of up to 100%, such as in composting plants where long chains are used, the change in length due to the tensile stress amounts to up to 8%. In a chain with a length of 100 m, the change in length adds up to 0.8 m.
As the energy transmission lines are connected to both the fixed base and the driver, the change in length of the chain due to tensile stress results in a difference in length between the energy transmission lines and the chain, meaning that the energy transmission lines are subjected to alternating tension. This tension has a particularly pronounced effect on the inside transverse members of the links in the deflection area of the chain. They are deformed and can even fracture.
When the chain is subject to compressive stress during the return or thrust travel of the driver, the chain tends to rise up in the area of the upper strand, i.e. the upper part of the bent chain, and to overlap, even if only weak upward force components act on it. The bending stresses that occur in the joint area of the overlapping chain links are then so high that the chain can easily break in this area.
An energy guiding chain of the kind specified in the opening paragraph is known from DE 26 09 451 B2. The inextensible elements, which are flexible in the bending direction of the chain, are mounted in the form of a cable or a chain on the underside of the chain links or transverse members, separately from the articulated joints. They serve to prevent the chain from sagging in the direction opposite the bending direction of the chain. Consequently, no stops are required for this purpose. Instead, the individual chain links of the upper strand are firmly pressed together and held in extended position by the inextensible element provided on the underside of the chain links. However, a self-supporting upper strand of this kind is not suitable for relatively long chains with relatively long travel paths.
In order to keep the upper strand stretched, the inextensible element must be mounted on at least every other chain link, as sagging cannot be prevented if the intervals are any greater. However, mounting the inextensible element on at least every other chain link makes manufacturing considerably more complex. Mounting the inextensible element on every other chain link is also a disadvantage in that the chain cannot relax sufficiently in the deflection area.
In order to keep the upper strand stretched, it is further necessary to pre-tension the inextensible element in the longitudinal direction of the upper strand. Because of this pretensioning, there is a tension difference between the chain and the inextensible element, particularly during thrust motion of the upper strand, which causes an upward force component. As mentioned above, there is a danger of the chain links of the upper strand rising up when the chain is under thrust, this possibly leading to the fracture of the chain in this area.
If the chain links are made of plastic, tension differences between the chain and the inextensible element that lead to an upward force component can occur particularly as a result of the thermal expansion of the plastic.
Therefore, an object of the present invention is to design an energy guiding chain in which a change in length due to tensile stress can be avoided relatively simply, even at high temperatures and high humidity, and in which the rising of the upper strand under tensile stress is prevented.
This object can be achieved by an energy guiding chain of the type specified in the opening paragraph in which the chain links, in several sections of at least three links, and the driver are fixed to the inextensible element(s) in such a way that forces transmitted by the fixation to the chain links act approximately at the level of the pivoting axes of the chain links and the tension of the element(s) in the longitudinal direction of the chain falls towards zero when the chain is thrust by the driver or comes to a halt after a thrust.
The fact that the chain links are mounted on the inextensible element(s) in sections of at least three chain links ensures sufficient relaxation of the chain in the deflection area. As the forces transmitted to the chain links through the mount act approximately at the level of the pivoting axes of the chain links, tension differences between the chain and the inextensible element(s) cannot cause an upward force component that could be feared to cause the upper strand to rise under thrust against the weight of the chain and the energy transmission lines. The tension of the inextensible element(s) is adjusted in such a way that, when the chain is thrust or comes to a halt after a thrust, only little or no force acts on the articulated joints of the chain links, so that, in particular, the pivoting motion of the chain links in the deflection area is not restricted.
Energy guiding chains are already known (DE 94 09 082 U1, DD 249 742 A 1, DE 1 131 480 C1) in which the chain links are connected to one another in a central area by inextensible elements that are flexible in the bending direction of the chain. Due to their flexibility, the inextensible elements form articulated connections between the chain links instead of overlapping joint areas. In these chains, however, the inextensible elements are not mounted to the chain links at intervals of at least three chain links and to the driver. Furthermore, the publications in question do not indicate that the tension of the inextensible element(s) in the longitudinal direction of the chain tends towards zero when the chain is thrust by the driver or comes to a halt after a thrust.
In a preferred configuration of the invention, the chain links are mounted on the inextensible element(s) in sections corresponding to at least the arc length extending over 180xc2x0 of the deflection area of the chain.
The forces transmitted through the mounting to the chain links preferably act within an area that is approximately at the level of the pivoting axes of the chain links and extends one-quarter of the link height above and below the level of the pivoting axes. It is particularly advantageous for the forces to act within an area that extends one-sixth of the link height above and below the pivoting axes.
The sections in which the chain links are mounted on the inextensible element(s) can be of identical or different length. Preferably, various lengths are used and the sections become smaller towards the driver, because the tensile stress of the chain increases towards the driver.
There are preferably between 2 and 5 sections per 50 m chain length.
The chain link of the section-wise division that is nearest to the driver is preferably not the chain link directly adjacent to the driver, but rather a chain link positioned at a distance of several chain links away that forms the end of the first section.
The part of the chain, adjacent to the driver, in which the inextensible element(s) is/are arranged, preferably extends over the entire upper strand and the bending area of the chain and into the lower strand when the chain is in a central position of travel, in which the upper strand and lower strand are of roughly the same length.
The inextensible element, or at least one of the inextensible elements, is preferably positioned roughly in the middle of the inside of the chain. At least one element can also positioned to the outside within the chain, in the vicinity of the plate-links.
In particular, the element, or at least one of the elements, can be a steel cable. Steel cables have the advantage that they have very low extensibility and can be bent without generating tension. However, any other element that displays these properties can also be used. For example, a metal chain, a horizontally arranged metal strip or an inextensible, flexible belt can also be used.
As the bending of the steel cable, or of any other corresponding element, in the bending area of the chain occurs without tension, the steel cable is relaxed in this area, so that the bending of the chain is not restricted by the steel cable. In the upper strand of the chain, where tensile forces act when the chain is pulled, the steel cable or corresponding element is taut in the longitudinal direction of the chain, meaning that it can absorb the tensile stress when tensile forces begin to act on the chain.
In a preferred configuration of the invention, adjacent ones of the chain links located at the ends of the individual sections are connected to one another and, of these, the chain link nearest to the driver is connected to driver, in such a manner as to resist stretching, by at least one element that is inextensible in the longitudinal direction of the chain and flexible in the bending direction of the chain.
Two taut cables or corresponding elements are preferably positioned between each pair of adjacent chain links located at the ends of individual sections and between the one of these chain links nearest to the driver and the driver.
The inextensible element(s) is/are preferably mounted on rails located separately from the transverse members that are connected to the opposite plate-links of the chain links.
In an expedient embodiment of the invention, the energy transmission lines guided in the chain are mounted on these rails by means of clamping blocks, and the rails also have mounting elements for the ends of the steel cables or other corresponding inextensible elements.
The rails can have pins on their ends, which lie in the transverse direction of the chain, that act as the link pins of the associated chain links. This means that the pins on the rails positively engage two flush openings in the overlapping areas of two adjacent chain links and thus form the pivoting axes of these chain links. This arrangement permits the energy transmission lines and separate, inextensible elements mounted on the rails to be arranged in oscillating fashion about the pivoting axes.
In another, preferred configuration, the ends of the rails lying in the transverse direction of the chain have projections that engage correspondingly designed grooves on the insides of the chain links between the joint areas. This arrangement permits the use and replacement of the design according to the invention without changing the associated chain links in any other way. The grooves provided in all chain links of a chain series can also be used for mounting other parts between the plate-links.